The present invention relates to an image forming material that is used in electrophotography of, e.g., printers, plain paper copiers, and facsimile machines, thermal transfer recording, writing tools, and printing and can be erased after image formation.
With the recent progress of office automation, the amounts of various pieces of information are significantly increasing, and information output is increasing accordingly. Information output is represented by display output and hard copy output from printers to paper sheets. Display output requires large-scale circuit boards in display units and hence has problems in portability and cost. Hard copy output is the most basic image display means and superior in versatility and storage stability. However, hard copy output uses large amounts of paper as a recording medium when the information amount increases, and this leads to an increase in deforestation. Forest resources are very important to maintain the terrestrial environment and suppress the greenhouse effect caused by carbon dioxide. Therefore, it is an important subject to minimize future deforestation and efficiently use the paper resources that we presently possess.
Conventionally, paper resources are recycled by processing sheets of paper on which image forming materials are printed using large amounts of a bleaching agent and water and remaking paper fibers to manufacture recycled paper with low paper quality. This method raises the cost of recycled paper and causes new environmental pollution resulting from waste liquor disposal.
Formerly, paper sheets are reused by correcting images using rubber erasers to pencils and ink erasers to writing inks. However, these methods have low correction efficiency, and the reuse itself has its limit. Recently, rewritable paper has been proposed to reuse hard copy paper sheets. Unfortunately, this rewritable paper is applicable only to thermal recording and is not recyclable, although it is reusable, because it is special paper.
The present inventors are developing an image forming material that contains a color former, a developer, and a decolorizer compatible with these components, can form images in the same manner as common image forming materials, and allows formed images to be erased by processing the material with heat or a solvent. Use of this erasable image forming material makes it possible to repeatedly reuse paper sheets any number of times by returning the paper sheets to blank paper sheets by erasing images, with minimum degradation of paper quality. Since recycle need only be done when the paper quality significantly degrades by the reuse, the use efficiency of paper resources greatly improves. In this manner, the essential paper use amount can be reduced, so deforestation can be minimized. Additionally, it is possible to minimize any increase in cost of recycle paper and the environmental pollution by waste liquor disposal, that are problems in the present recycle system.
The image forming material being developed by the present inventors and containing a color former, a developer, a decolorizer, and a binder resin can form images in the same manner as common electrophotographic toner and can be erased by a solvent or heating. However, this image forming material sometimes varies the image reflection density depending on the manufacturing lots or causes defective fixation (offset) when images are thermally fixed. Also, when images are erased with a solvent, marks of a flow of the image forming material or blurred images partially form, and unerased images sometimes remain. Since these unerased images limit the reuse of paper sheets, the material must be improved to be able to decolor formed images as completely as possible.
Also, depending on the intended use of the image forming material, it is preferable to be able not only to completely erase images but also to repeatedly write and erase images. Accordingly, an image forming material applicable to such a use is also being demanded.